1. Field of the Invention
The present invention relates generally to accessory control devices used to change the functions or operating features of various types of existing electronic apparatus, and more particularly to an accessory device that selectively alters target apparatus operating characteristics according to whether or not it is installed. The invention further relates to information processing apparatus and methods that employ accessory control devices.
2. Related Technological Art
In recent years, digital electronic equipment, such as, personal computers, word processors, work stations, and other electronic equipment using built-in microprocessors, such as printers, facsimile machines, memo devices, musical instruments, cooking equipment, and cameras, has found extensive use throughout large segments of society. In addition, other widely used equipment such as automobiles, robots, numerically controlled machines, and a variety of other electrified products, now make use of microprocessor technology.
The application of programmable digital logic to equipment operation provides a potential of more flexible control as compared to that obtained with simple feedback controls previously used with various fixed hardware designs. In addition, using programmable logic, essential operating functions are altered by simply changing command software. One advantage of this approach is that totally different control operations are obtainable for a given piece of equipment or hardware by simply modifying the contents of program storage or memory elements, such as ROMs, that store specific processing or program steps. This new material can even be loaded as a new program from an external device such as a floppy disk. Moreover, smaller incremental changes in function, such as design revisions, can be advantageously implemented by only upgrading software.
However, the ultimate capabilities of processor controlled electronic equipment are determined by the capabilities of the processor itself. That is, each processor is itself finally limited by operating characteristics such as the maximum number of processing steps obtainable per unit time, the maximum number of data bits that can be processed at one time, the width of any data or command transfer buses, and so forth. As a result of these limitations, achieving improvements by merely upgrading software versions is at best limited to improving equipment ease of use. In reality, it has not been possible to achieve large improvements in operating features for existing electronic equipment.
At the same time, improving or upgrading software versions often requires replacing a ROM or other memory element containing the software. It is much more difficult to obtain access to or change software when replacement of such code containing ROMs is required. As a result, revising software to improve equipment operation is actually very difficult unless the particular piece of electronic equipment is already scheduled for a ROM exchange, different ROM version, at the time of its initial design, or unless the software can be supplied on a replaceable medium such as a flexible disk and used to modify stored program material.
Furthermore, once equipment operation is altered to improve or add to functionality by replacing a ROM, it is difficult if not impossible to return the functions to their original operating states. In actual use, there are few cases in which there is a desire to return functions that have simply been improved to their original state or condition, but when functions are changed or added to, there are situations in which an equipment user may want to return to an original status or condition, such as for software compatibility or speed. This problem is discussed further below using a page printer as an example.
In recent years, page printers, such as laser printers, have enjoyed widespread distribution and are rapidly becoming the leading device for high-speed data and image output from computers. Laser printers typically provide high image resolution (200 to 800 dpi) and high printing speed on the order of several pages a minute, which are desirable characteristics. Many laser printers allow the installation of an "add-on" or "accessory" cartridge in which fonts or programs are stored in a built-in ROM. When a cartridge with a stored program is installed, new functions, such as data processing functions using a Page Description Language (PDL), may be added to the laser printer capabilities. However, when such cartridges are installed, the laser printer typically can no longer utilize all of its original functions and becomes a dedicated printer for the accessory device, outputting print data using the ROM program. In this example, the printer outputs image data according to a prestored PDL program or data. More particularly, in laser printers that store various operating conditions or parameters in a rewritable nonvolatile memory (e.g., EEPROM), when a cartridge is installed the contents of that memory may be rewritten to effect or better match the interface with the new accessory device and its programming. In this latter situation, the operating parameters or conditions cannot be completely recaptured or recalled even if the cartridge is removed.
This problem cannot be overlooked as an undesirable situation in many applications for various types of electronic equipment such as printers, facsimile machines, electronic pocketbooks, musical instruments, cooking appliances, cameras and other consumer electronic products having a built-in microprocessor, or in electric equipment for use in automobiles, robots, machine tools and other industrial electronic devices, and various types of electrical equipment in which functional changes are performed by also affecting stored parameters or operating conditions.
What is needed is a new method and apparatus for interfacing an accessory control device or circuit, especially of the plug-in cartridge-type, with a variety of electronic systems or apparatus that allows substantially all of an original operating database or operating parameter set to be recalled when desired or needed. This would allow for resetting an apparatus to an original operating status or operating state when the accessory control device is disconnected.